The present invention relates to a motion translation system for converting continuous rotary motion into reciprocating linear motion, and more particularly to such a system which reduces the vibration arising out of the rotational imbalance of the conventional assembly.
U.S. Pat. No. 3,260,289, issued Jul. 12, 1966, is directed to a saber saw attachment which includes a motion translation system for converting the rotary motion of a shaft member into the reciprocating linear motion of a piston member. FIG. 1 hereof is a reproduction of FIG. 2 of the patent and shows, among other components, a hollow housing member 12, a piston member 28, a shaft member 14, and a single ball bearing 46. The housing member is hollow and open at each end. The piston member is slidably and non-rotatably supported within the housing and has means at the front end for removably receiving a saber saw blade or the like and a central longitudinal opening in the rear end thereof. The central longitudinal opening of the piston member has a bearing raceway formed therein which is substantially semicircular in cross-section and positioned substantially in a plane perpendicular to the longitudinal axis of the piston member. The shaft member is rotatably supported in the housing member and has a portion thereof extending exteriory of the rear end of the housing and a portion thereof extending slidably within the longitudinal opening of the piston member. The shaft member has a circumferential raceway formed in the exterior surface thereof, the raceway being substantially semicircular in cross-section and positioned substantially in a plane at an angle to the axis of the shaft member. A single ball bearing is positioned within the piston raceway and the shaft raceway. For further details, see U.S. Pat. No. 3,260,289, the substance of which is incorporated herein by reference. The specification mentions that a diametrically opposed pair of ball bearings may be used when a double-acting raceway (that is, a raceway which makes two back-and-forth oscillations in one revolution of the shaft) is desired.
Vibration is caused by many variables and deemed unavoidable in many mechanical systems. Common sources of vibrations are imperfections of components, wear from usage, and errors in installation (due to linkage and/or housing/shaft fittings). Other contributors are speed above resonant frequencies, insufficient stiffness of the assembly, and unbalanced forces of the system.
The current approaches used to address vibrations are to improve the manufacturing techniques, to add wear-resistance properties to the system, and to improve the mounting/coupling methods. Reduction of mass in the system will produce different frequencies, thus resulting in an "acceptable" vibrational level. Also, adding a vibration-absorption system can further reduce the amount of vibrations. These approaches are part of the improvement to any mechanical system.
When these approaches do not reduce vibrations sufficiently, other methods should be employed. From simple mechanics of motion, unbalanced forces contribute directly to the vibration level, and at times are detrimental to the system. By reducing or eliminating these unbalanced forces, the system vibration level should be minimized.
In the continuous rotary-to-reciprocating linear motion translation system, the forces change dynamically due to the imbalances of the design. Adding a counterbalance is an idea suited to address this issue. However, an ideal counterbalance needs to vary and to adjust itself to these changing forces.
Perhaps the best example of this counterbalance application would be the conventional crank shaft-piston connecting rod transmission system. Here, the counterbalancing weights are located and integrated into one side of the crank shaft. The pivoting rollers (or bearings) to drive the connecting (piston) rod are also positioned and integrated into the crank shaft, but on an opposite side of the crankshaft and eccentric to the center of the crank shaft rotation. As the crank shaft rotates, the eccentricity of pivoting rollers and the movement of the connecting rod generate unbalanced forces. The one sidedness of the counterbalance weights then generate opposing forces to cancel the unbalanced forces of the pivoting rollers and connecting rods assembly. Thus the vibrational level of the engine is not as high as it would have been without the counterbalance.
Most known counterbalance systems move about the axis of rotation and direct the opposing forces perpendicular to the axis of rotation.
Accordingly, it is an object of the present invention to provide a motion translation system having a counterbalance which does not move about the axis of rotation.
Another object is to provide such a system which directs the opposing forces linearly in the opposing directions of the piston member or reciprocating linear motion driver and the counterbalance, thereby to provide linear motion of each parallel to the axis of rotation.